Systems and methods for mapping the ocular surface

ABSTRACT

Examples of methods and apparatus for an accurate measurement of the anterior surface of the eye including the conical and scleral regions are disclosed. The measurements provide a three-dimensional map of the surface which can be used for a variety of ophthalmic and optometric applications from astigmatism and keratoconus diagnostics to scleral lens fitting.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/535,925, filed Nov. 7, 2014, entitled “SYSTEMS AND METHODS FORMAPPING THE OCULAR SURFACE,” which claims the benefit of and priority toU.S. Provisional Patent Application No. 61/962,449, filed Nov. 8, 2013,entitled “SCLERAL TOPOGRAPHY MEASUREMENT DEVICE,” both of which arehereby incorporated by reference herein in their entireties.

BACKGROUND

Technical Field

The present disclosure relates to three dimensional imaging using thestructured light approach, and more particularly to ocular surfacemeasurement over the anterior surfaces of the cornea and sclera.

Description of Related Art

The accurate knowledge of the corneal surface is very important fordiagnostics and treatment of a number of ocular conditions. Cornea isresponsible for about 70% of the refractive power of the eye andtherefore the corneal topography has a great importance in determiningthe quality of vision. It is commonly used for diagnosis of keratoconus,for selecting appropriate soft contact lenses, for fitting sclerallenses, and for topography guided Laser-Assisted in situ Keratomileusis(LASIK).

Currently the majority of the corneal topography is performed using aPlacido disk. The concept of the Placido disk was introduced by AntonioPlacido in 1880 and since then it has been the primary method forcorneal topography. The method is based on viewing or imaging thecorneal reflection of series of concentric bright and dark ringspositioned in front of the cornea. By increasing the number ofconcentric disks and placing them on a concave surface around the eye,it is possible to measure a large section of the cornea. But in mostcases the data on the central zone needs to be interpolated and the dataon the corneal periphery is often missing due to limited reflection.Additionally, Placido disks are not capable of measuring the scleraltopography, which is important for custom fitting of scleral lenses.

In addition to the Placido disk, scanning slit systems, such as theOrbscan II by Bausch & Lomb, Scheimpflug systems such as the Galilei byZeimer Ophthalmic Systems, and rastersterographic systems such as theCTS by Par Technlogies have been used for corneal topography. Whilethese systems provide better measurement of the corneal apex they lackthe coverage of the corneal periphery and sclera needed for scleral lensfitting.

SUMMARY

The present disclosure describes an advanced coded-light measurementsystem for mapping the complete three dimensional anterior ocularsurface. Commonly used ocular topography measurements, includingPlacido-disk measurements, scanning slit beam measurements, andrastersterographic measurements have focused on the central region ofthe cornea. Extending such measurements to the entire anterior surface,specifically to include the sclera, introduces a new set of challenges.These include: the dissimilar optical properties of the sclera and thecornea, interference of the eyelids which can occlude significantportions of the desired measurement region even when manually retracted,and the periodic involuntary microsaccadic eye movements.

A sample embodiment of the technology disclosed herein provides a set ofpossible solutions that can be used together or independently to addressone or more of the above challenges. In the said embodiment a singlelight projector is positioned to direct light towards the ocular surfaceand two or more imaging sensors are positioned to image the eye surface.

In the said embodiment the surface of the eye is coated with afluorescent dye and the projector is configured to project light in awavelength that overlaps the excitation band of the said dye. Theresulting fluorescent light emitted from the dye covering the ocularsurfaces is detected using imaging sensors. Using the above fluorescentimaging method solves the complication of dissimilar reflectiveproperties of scleral and conical surfaces.

In the said embodiment the projected light is comprised of coded lightsequence. This sequence contains series of structured light patternswhich can be interpreted as time-series measurements, where theprojected intensity at a given location over time has a unique patternfor each pixel or subregion of pixels, allowing accurate, unambiguousidentification of triangulation points in each member of thestereo-photogrammetric pair. Said triangulation measurements performedin order to obtain the three dimensional surface of the eye can beperformed between two cameras or between one of the cameras and theprojector. The abovementioned triangulation measurements can beperformed separately or in any combination of the above in order toincrease measurement redundancy and reduce the measurement errors. Saidcoded-light sequences allow higher resolution measurements thanconventional raster-stereographic methods by coding all pixels in thepattern region, instead of requiring interpolation between grid lines orgrid intersection points.

In conventional coded light mapping of a surface topography a care istaken so that the measured object does not move during the measurement.Microsaccadic movements are involuntarily movements of the eye thatoccur once or twice every second. Therefore, it is advantageous to takethese movements into account during the three dimensional mapping of theeye. One embodiment of the disclosed technology uses multiple wavelengthillumination of the eye during the structured light imaging. Onewavelength can be used for excitation of the fluorescent dye duringcoded light imaging, while another wavelength or wavelengths can beselected so the features on the eye surface, including but not limitedto the blood vessels and limbus can be resolved in the recorded images.The said light of different wavelengths can be projected onto the eyesimultaneously or in sequence. In one embodiment of the disclosedtechnology the light of the said wavelengths can be projected before andafter the coded light sequence. In said embodiment locations of theocular surface features in the images before and after the projection ofthe coded light can be compared to ensure that eye did not move duringthe measurement and the data set can be used for three dimensionalsurface reconstruction.

Embodiments herein allow for measurement of the complete anterior ocularsurface, including regions which may be occluded by the eyelids evenwhen said eyelids are retracted manually, by combining multiplemeasurements of the ocular surface taken for different gaze directionsof the eye. Each of said multiple measurements produces a partialsurface model of the visible region of the ocular surface, includingthree dimensional surface coordinates and color or intensitymeasurements. Feature information from the color or intensity componentof the model is used to aid convergence of the model registrationprocesses, allowing the smooth surfaces of the multiple said partialsurface models to be uniquely registered in space into a complete modelof the full anterior ocular surface.

In other implementations, the object being mapped need not be a human oranimal eye and may be any other type of surface. The disclosed systemsand methods may be advantageous for mapping a surface of a moving orunstable object (biologic or non-biologic).

Other features and aspects of the disclosed technology will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, thefeatures in accordance with embodiments of the disclosed technology. Thesummary is not intended to limit the scope of any disclosures describedherein, which are defined solely by the claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Throughout the drawings, reference numbers may be re-used to indicatecorrespondence between referenced elements. The drawings are provided toillustrate example embodiments described herein and are not intended tolimit the scope of the disclosure.

FIG. 1a is a schematic illustration of an example of astereo-photogrammetric triangulation between single camera and singleprojector

FIG. 1b is a schematic illustration of an example of astereo-photogrammetric triangulation between two cameras.

FIG. 2 is an illustration of an example of a system for measuring theocular surface.

FIG. 3 is an illustration of an example of an optical head arrangement

FIG. 4 includes example images of the structured light illuminated eyetreated with fluorescein dye.

FIG. 5a includes example images illustrating one possible structuredlight illumination sequence incorporating flat-field frames for ameasurement system operating in Discrete Station Mode

FIG. 5b includes example images illustrating a possible structured lightillumination sequence incorporating flat-field frames for themeasurement system operating in Continuous Processing Mode

FIG. 6 is an illustration of use of fixation targets to acquire data formultiple gaze directions for the purpose of mapping the ocular areaunder the eyelids

FIG. 7 is a flow chart illustrating an example focusing process

FIG. 8 is a schematic illustration of triangulation options offered by amultiple camera, single projector measurement arrangement.

FIG. 9 is a flow chart illustrating an example data acquisition process.

FIG. 10 is an illustration of sample coded light encoding sequences

FIG. 11a is flow chart depicting an example of a templated grid searchalgorithm.

FIG. 11b is an illustration of examples of data products at variousstages in a sample templated grid search.

FIG. 12 is an example of the measured 3D surface of the eye surfaceobtained by manually retracting the eyelids

FIG. 13 is a flow chart depicting a sample stitching algorithm forcombining three dimensional surface models obtained at multiple gazedirections for the purpose of mapping the surface of the eye under theeyelids.

FIG. 14 is an illustration demonstrating examples of intermediate andfinal results of the stitching algorithm for mapping the surface of theeye under the eyelids.

FIG. 15 is a flow chart depicting a sample iterative data acquisitionprocess for operating in Discrete Station Mode.

FIG. 16 is a flow chart depicting an example processing tree forDiscrete Station Mode

FIG. 17 is a flow chart depicting a sample measurement process forOperation of Continuous Processing Mode

FIG. 18 is an illustration of one arrangement of an ocular topographercombining a Placido disk with a structured light system.

DETAILED DESCRIPTION

The present disclosure is directed toward systems and methods forperforming surface measurement, mapping, and modeling of the completeanterior surface of the eye, including the conical and scleral regionsof the eye.

Commonly use ocular topography measurements have focused on cornealtopography and include: Placido disk measurements which using concentricilluminated rings to map the surface slope and infer topographyelevation measurements from the slopes based on specific assumptions,scanning slit measurements which use using moving laser line or slitbeam triangulation methods to calculate the elevation topography, andrastersterographic measurements which triangulate points from a staticpattern projected on the ocular surface and interpolate between thetriangulated points. Scanning slit and rastersterographic methodstypically employ stereo-photogrammetric measurement pairs which maycomprise a light-source 0102 and an imaging detector 0103 with knownorientations relative to the surface to be measured 0101, as depictedschematically in FIG. 1a , or may comprise two imaging detectors 0105and 0106 with known orientations relative to the surface to be measured0104, as depicted in FIG. 1b . Calibration of the stereo-photogrammetricpairs allows accurate triangulation of points in three dimensional spacefrom the two-dimensional locations of the points in the imaging planesof the respective light source or imaging detectors.

According to some embodiments of the technology described herein, asystem for mapping and modeling of the ocular surface can include anoptical measurement head comprised of a pattern projection system, twocameras, and a fixation target array for fixing the gaze direction ofthe subject during the series of measurements, a mounting system for theoptical measurement head comprising a mounting stand attached tomanipulator with a chin and forehead rest for controlling the relativeorientations of the eye of the subject to be measured and the opticalmeasurement head, a computing device connected to the measurement headfor controlling measurement acquisition and processing the acquireddata, and a display screen. FIG. 2 shows the schematic drawing of oneembodiment of the technology described herein, including an optical head0201, a manipulator comprising a moveable optical stand 0202, a chinrest 0205, a forehead rest 0206, an attached computing device 0203, anda display screen 0204 (which may include computer processing hardwareconfigured to implement the analysis methods disclosed herein).Optionally, in some embodiments, the technology can be in communicationwith a scleral contact lens manufacturing system 0207, which can utilizeinformation related to the topographic map of the eye generated by thetechnology for diagnosis or customized treatment of the subject's eye orfor manufacturing of a scleral contact lens for the subject's eye. Thescleral contact lens manufacturing system 0207 can be geographicallyremote from the rest of the system, and the topographic map informationcan be communicated to the manufacturing system 0207 via a networkconnection (e.g., the Internet, a local or wide area network, etc.).

FIG. 3 shows the internal structure of one embodiment of the opticalmeasurement head. Referring now to FIG. 3, the pattern projection systemcomprising a digital light processing (DLP) or liquid crystal device(LCD) projector 0305 and an optical beam-shaping assembly 0306 islocated in front of the eye so that the surface of the eye is within thefocusing depth of field of the projected pattern image. In otherembodiments, any type of micro-mirror device, microelectromechanicalsystem (MEMS) device, or spatial light modulator can be used. A seriesof structured light patterns are projected onto the surface of the eye,wherein the tear film is stained with a fluorescing substance such asfluorescein. The pattern projection system produces structured lightpatterns and flat-field illuminations in at least two wavelength bands,chosen such that in some wavelength band the projected wavelength rangeoverlaps with the excitation wavelength of the fluorescent substance butnot the fluorescence wavelength of said fluorescent substance, and inanother wavelength band the projected wavelength range overlaps thefluorescence wavelength of the fluorescent substance but not theexcitation wavelength of said fluorescent substance. This is achieved byeither utilizing optical filters in the projection optical path or byusing a narrow wavelength multi-LED (light emitting diode) light sourcewithin the projector, where at least one LED in the multi-LED lightsource corresponds to each of the required wavelength bands previouslydescribed. The projection of a structured light pattern onto theanterior surface of an eye stained with said fluorescent substanceresults in fluorescence of the eye surface in accordance with theincident structured light pattern projection. This fluoresce is imagedusing two charge coupled device (CCD) or complementarymetal-oxide-semiconductor (CMOS) cameras 0301 and 0302 positioned at acertain angle on each side of the projector. The focusing depth of fieldof the camera optics is chosen to correspond with focusing depth offield of the pattern projection system optics so that a clear image ofthe fluorescence grid lines on the anterior ocular surfaces is obtained.In this embodiment, the optical system of each camera 0303 includes afluorescence emission filter 0304, which allows imaging the fluorescencesignal without the interference from the reflected portion of theexcitation light that is output by the projector. Camera operation issynchronized with the projector output so that one or more images arerecorded by each camera for each of the frames in the projectedstructured light pattern sequence. In some embodiments, illuminationlevels incident on the ocular surface are less than 3.9×10⁻³ Joules ofradiant energy as measured through a 7-mm aperture located within 5 mmof the projector focus.

In one embodiment described herein the projected structured lightpattern sequence is comprised at least in part of a series ofinterchanging vertical and horizontal grids of parallel lines. FIG. 4shows the sample fluorescence images resulting from projecting saidgrids onto the eye surface. The images presented are recorded by the twocameras in the optical measurement head, one of which is located on theright side of the optical axis of the projector 0401 and the otherlocated on the left side of the optical axis of the pattern projectionsystem 0402.

In some embodiments of the technology described herein, the projectedstructured light pattern sequence also comprises additional flat-fieldframes which may precede the projected structured light pattern grids,follow them, or both. In these flat-field frames the eye is illuminatedby a uniform or almost uniform light with a wavelength that overlaps thetransmission wavelength of the fluorescence emission filter located inthe optical path of the cameras but does not overlap the excitationwavelength of the fluorescent substance introduced into the tear film. Asingle image or several images are recorded by each camera during thesaid flat-field illumination of the eye. In some embodiments, theseemission wavelength flat-field illumination images recorded before andafter an excitation wavelength sequence of projected structured lightpatterns can be used to verify that the eye has not moved during themeasurement and for correction of measurement artifacts caused by anysuch eye movement. Since it has been reported that the microsaccadicmovements of the eye involuntarily occur with a periodicity between 0.3and 1 seconds it can be advantageous that the entire measurementsequence should last less than about 0.5 second. In embodiments wheremultiple frame structured light sequences are employed, emissionwavelength illumination imaging can be used to verify that the eyehasn't moved during the measurement sequence. A sample sequence ofimages showing flat-field emission wavelength illumination imagesbracketing a sequence of several excitation wavelength structured lightillumination images is presented in FIG. 5 a.

In some embodiments, the structured light sequence duration can beshortened by projecting multiple illumination patterns simultaneously innon-overlapping wavelength bands, employing color imaging systems, andemploying hardware and software filtering to isolate each pattern in theprocessing. In such embodiments, the structured light sequence durationcan be as short as a single camera frame, typically five milliseconds orless.

Some embodiments can be used for mapping the surface of the eye in orderto create a custom back surface of the scleral lens for a comfortablefitting. For said application it can be advantageous that a measurementof the ocular surface is performed within a 12 mm to 22 mm diametercircle centered at the cornea apex. For such large diameters theportions of the scleral and corneal surfaces may be hidden behind theeyelids, therein complicating the measurement procedure.

In some embodiments, a fixation target array can be used to guide thegaze direction of the subject during the surface measurement processsuch that measurements are taken with the eye oriented at each of aplurality of gaze directions, such that each measurement comprises dataof a different portion of the ocular surface. In said embodiments thelocation of each element in the fixation target array is chosen so thatthere is a significant overlap between measurements that can be used forlater manual or automated stitching of the plurality of measurements inorder to obtain a single composite model of the eye surface within 12 mmto 22 mm diameter region centered at the corneal apex, which may includeregions of the ocular surface normally hidden by eyelids. FIG. 6 depictsa measurement process comprising measurements of the eye 0602 fixed atthree gazed directions corresponding to three different illuminatedelements in the gaze fixation target array 603, 607, 611. Flat-fieldillumination images captured at each gaze direction are depicted in 06010605 and 0609.

In the abovementioned embodiments the manual or automated registrationand stitching of the resulting three dimensional datasets taken at eachgaze direction can be performed either by optimizing correspondencebetween the three dimensional shapes and features in each dataset asmeasured using fluorescence wavelength illumination, or by combiningsaid optimization of correspondence with three dimensional shapes withcolor or monochrome intensity feature information for optical surfacefeatures such as the corneal limbus and blood vessels obtained duringflat-field illumination.

In some embodiments alignment and focusing can be achieved by providingthe operator of the system with a real time display from one or morecameras during the manual focusing procedures. The focusing procedurecan then be separated into two distinct steps. The sequence of thesesteps is described in FIG. 7. In the first stage the eye is illuminatedwith a dim light 0701 with the wavelength overlapping the emissionwavelength of the fluorescent substance and the transmission wavelengthof the bandpass filter installed in the optical path of the camera.During this stage the eye image is viewed on the display and is centeredand focused in the camera field of view by manually adjusting theposition of the optical measurement head using the manipulator 0702. Inthe second step a cross or other focusing pattern is projected by theprojector 0703 operating in the wavelength of the fluorescenceexcitation of the fluorescing substance that was used to dye the tearfilm and the eye surface. As the position of the optical measurementhead is adjusted by means of the manipulator, the location of focusingpattern in the fluorescence image of the eye shifts in the camera'svision frame, and hence on the display screen. The physical position orthe optical head is adjusted forward or backward 0704 until the apparentposition of this fluorescence focusing pattern on the display screenoverlays a corresponding fixed focusing guide pattern which is alsodisplayed on the device screen. When the fluorescence image focusingpattern and the fixed focusing guide pattern are co-located on thedisplay screen, the eye is correctly centered in the optical depth offield of all relevant optical systems. Additional confirmation of thefocusing state is provided to the operator by means of variations incolor of the fixed focusing guide pattern. This procedure allows forfast, very accurate focusing of the eye for the performance of themapping procedure.

In some embodiments the intensity of the fluorescence can be evaluatedduring or after the focusing process and a visual or auditory indicationcan be used to alert the operator of the state of the fluorescent dye onthe ocular surface. In the case of insufficient dye the operator can beprompted to add more dye to the eye before continuing with themeasurement.

During the operation of the device in all of the abovementionedembodiments the intensity of the illumination for the fluorescence andemission wavelength is selected so that it does not exceed the safetylimits established by appropriate standards.

In one embodiment described herein the pattern projection system can becapable of projecting one or more sequential predeterminedtwo-dimensional patterns, whereas first and second cameras may be stillor video CCD, CMOS or other cameras. The herein topography systemcomprises between one and three simultaneous stereo measurements.

In another embodiment, a method for aligning and focusing a topographicmapping device for an ocular surface of an eye of a subject is provided.The topographic mapping device can comprise a projection system, one ormore imaging sensors and a display. The method comprises illuminatingthe eye with one or more structured alignment patterns, capturingreflected or fluorescence images of the one or more structured alignmentpatterns by the one or more imaging sensors, and displaying thereflected or fluorescence images in real-time on the display. Focusingof the topographic mapping device can be achieved by adjusting thedevice position such that a visible pattern in the reflected orfluorescence image of the structured alignment pattern visually alignswith a corresponding guide pattern which is displayed along with thecaptured reflected or fluorescence images on the display. The displaycan show indicators like color changes, text instructions, audio cues,etc. to instruct or inform the focusing and alignment process. In someembodiments, the method can include simultaneously or sequentiallyilluminating the eye with two distinct focusing patterns including aflat-field illumination and a structured alignment pattern. In some suchembodiments, the method can include visually aligning the device usingimages of the reflected flat field illumination. In some embodiments,the flat field illumination is projected in a wavelength range thatoverlaps a fluorescence wavelength of a fluorescent dye used to preparethe ocular surface of the eye but does not overlap an excitationwavelength of the fluorescent dye, and the structured alignment patternis projected in a wavelength range that overlaps the excitationwavelength of the fluorescent dye used to prepare the ocular surface butdoes not overlap the fluorescence wavelength of the fluorescent dye.

In the example embodiment depicted in FIG. 8, the first camera 0803 andsecond camera 0804 can be arranged to form a stereo-vision pair with afield of view encompassing the illuminated portion of the surface to bemeasured 0801 Herein the illumination from the pattern projection system0802 is used to index correspondence between each illuminated pixel inthe first camera to each illuminated pixel in the second camera, andwhere a three-dimensional stereo calibration of the stereo pair can beused to triangulate the pixel correspondences between cameras intopoints in Cartesian space.

In said embodiment, the first camera 0803 and the pattern projectionsystem 0802 can be calibrated to provide a coded light linked stereopair, the pixel identities in the projected pattern as determined by theprojected coded light sequence are indexed to the illuminated pixels inthe first camera, and where a 3D structured light calibration betweenthe pattern projector and the first camera can be used to triangulatethe matched pixels between the projector and the camera into points inCartesian space.

In said embodiment, the second camera 0804 and the pattern projectionsystem can be calibrated to provide a coded light linked stereo pair,the pixel identities in the projected pattern as determined by theprojected coded light sequence are indexed to the illuminated pixels inthe second camera, and where a three-dimensional structured lightcalibration between the pattern projector and the second camera can beused to triangulate the matched pixels between the projector and thecamera into points in Cartesian space.

In said embodiment, between one and three abovementioned stereomeasurement methods can be used simultaneously to provide between oneand three distinct measurements of the ocular surface. The obtainedmeasurements can then be combined, averaged, or otherwise mathematicallymanipulated in order to increase the measurement accuracy at the entiremeasurement region or at a specific portion of the ocular surface. Forexample, the triangulation between the projector and the right cameracan be used for measurement of the right side of the eye and thetriangulation between the projector and the left camera can be used formeasurement of the left side of the eye, while the triangulation betweenthe two cameras can be used for the central portion of the eye, andoverlap between the measurement regions can be used to achieve errorreduction.

Several other embodiments can be made by adding capabilities, features,or by changing the ocular target to other objects with potentiallyvarying surface topographies.

The measurement process for the some embodiments is depicted in FIG. 9,wherein the subject's eye is prepared with fluorescent dye 0901 andpositioned with respect to the optical head 0902. The computing devicethen calculates and checks focus and data quality metrics 0903 beforeinitiating the formal data acquisition. Formal data acquisition takesthe form of a loop 0904 wherein a frame of the structure light patternsequence is projected onto the ocular surface 0905 and the emitted orreflected light from the ocular surface is captured by each imagingdetector 0906 and transferred to the controlling computing device. Atthe conclusion of the formal data acquisition loop, the acquired imagesare processed into three dimensional topographical models of theanterior ocular surface 0907. These three dimensional topographicalmodels are then stored in the memory of the computing device 0908 andmay subsequently combined with other measurements or used to calculateoptometric data products of various types.

In some embodiments the sequence of structured light patterns iscomprised in part by a series of one or more two-dimensional coded lightpatterns which allow specific pixels or regions in the projected patternor combination of patterns to be indexed to specific pixels or regionsin images of the ocular surface taken under illumination by said codedlight pattern or combination of patterns.

Combinations of coded light patterns may uniquely encode each row andcolumn of the projector pixel array, or may uniquely encode tiledportions of the projector pixel array in a repeating manner and rely onknowledge of surface constraints such as smoothness and continuity toallow unique pixel codes to be established from repeating series. Anexample of the former approach is the traditional binary encoding scheme1001 depicted in FIG. 10, where a square wave pattern of ON=1 and OFF=0values is projected and each pattern in the sequence increases thefrequency of the pattern by a factor of two until the square wavepattern has a wave period of just two pixels. By examining thetime-series values at each pixel for the entire sequence, a unique codevalue is achieved for each pixel in the array.

An example of the latter approach can be a series of N frames containinga 2-d array of parallel stripes oriented along the columns of the pixelarray, and where every Nth column has value ON=1, and all other pixelsin the frame have value OFF=0. If for each subsequent frame in thesequence the columns are shifted forward by one pixel, by projecting theN frames and examining the time series values of the pixels for eachcolumn, it is apparent that the first N columns have unique values, andthen for the next N columns, the first N values repeat, and thisrepetition continues for each set of N columns until the far edge of thepixel array is reached. That is, for any given column code value, therecan be many columns in the pixel array that share that code. Forsurfaces with known constraints such as smoothness, continuity, radiuslimit, and the like, this ambiguity can be dealt with algorithmically.As illustrated in the example in 1004 using N=3, if the stripes in agiven frame are located on every Nth pixel, it is not strictly necessaryto project N frames, but rather N−1 frames are sufficient as a sequenceof all zeroes represents a valid code sequence. The advantage of such anapproach is to take advantage of computing power to limit the number offrames in the coded light sequence without sacrificing measurementresolution. As depicted in 1005, the addition of a key stripe frame 1003can be used in addition to surface constraints to further limit theambiguity inherent in the encoded repeating series.

Another encoding scheme similar to the traditional binary approach canbe used by projecting narrow stripes instead of bar or square wavepatterns, as illustrated in 1002. In such an approach the same periodincreases between frames can be used, and each column can again beuniquely encoded provided the surface is relatively smooth andcontinuous with only minor algorithmic steps by using the stripes of theN−1th image in the sequence to locate those in the Nth image. Theadvantage of this type of encoding scheme over the traditional binaryencoding scheme, or a comparable Gray Code approach, using bar or squarewave patterns of increasing frequencies is that it minimizes therequired dynamic range of the imaging detector by flattening theintensity of the illumination incident on the ocular surface, preventingblooming of illuminated features in the imaging detector and increasingthe measurement speed by eliminating the need to dynamically adjust theexposure and aperture values of the imaging detectors during themeasurement process.

In some embodiments the encoding schemes are based on grids of parallellines which shift in space on the projector frame during the encodingprocess. Such encoding sequences can be parallel vertical lines andparallel horizontal lines in sequential or alternating series where theshifting vertical lines are used to encode the column values and theshifting horizontal lines are used to encode the row values. Or theencoding sequence can be a shifting Cartesian grid composed of parallelvertical lines and parallel horizontal lines superimposed on the samepattern frame. In the latter case, the horizontal and verticalcomponents of the pattern can be isolated algorithmically via Fouriermethods.

In some embodiments, regions of the projector pixel array are uniquelyencoded and these regions repeat in a tiled pattern across the entirepixel array, which are algorithmically decoded in to unique code valuesfor each individual pixel as required by some of the surfacereconstruction methods described subsequently. The robustness of thedecoding process by which the repeating tiled pixel code sequence istransformed into a set of unique pixel codes for each and every pixel inthe array can be greatly enhanced by the use of a key stripe patternduring the coded light sequence projection, which guides the algorithm—aTemplated Grid Search.

In the Templated Grid Search, an example of which is depicted in theflowchart in FIG. 11a , a two-dimensional key mask 1103 is produced froma focusing pattern or key stripe image 1101 captured by illuminating theocular surface with a structured light key stripe pattern. This keystripe pattern is applied algorithmically to a structured light patternmask 1105 produced from an image captured by illuminating the ocularsurface with a structured light pattern composed of parallel lines 1104,where the key stripe image represents a subset of this second structuredlight pattern. The key stripe mask is used as a template by whichneighboring stripes in the sequence can by identified and numbered withtheir appropriate row or column value. Simply, the key stripe mask isshifted in space in a loop 1106 wherein the product between the shiftedkey stripe mask and the structured light pattern mask observed forsubsequent shifts and recorded in an array 1107. When the product ofthese two images passes through a local maximum, the neighboring stripein the parallel grid is reached, and the pixels in said neighboringstripe can be identified using the shifted key stripe mask as a templateto define the search area. The newly identified stripe 1108 then becomesthe key stripe which is used as the template to find the next stripeover, in a continuing fashion. Each newly found stripe is assigned aunique stripe number in a modified version of the structure lightpattern mask 1109, which can then be converted into the bin array 1111through simple value latching. This approach allows the algorithm toeasily overcome gaps and intensity variations in fluorescein coverageand similar data faults. The approach is also very robust for a widevariety of surface topologies with no foreknowledge of the surfaceproperties, allowing wide latitude in the positioning and orientation ofthe target surface in the field-of-view of the measurement system. FIG.11b provides examples of the key stripe image 1101 b, the extracted keystripe template 1103 b, the structured light illuminated eye 1104 b, andthe structured light pattern mask 1105 b. The key stripe template 1103 bis iteratively shifted and applied to the structured light mask 1105 b,and the search product 1107 b is evaluated to determine the location ofthe next stripe. The gray scale intensity in the resulting masks 1109 band 1111 b illustrate the decoded stripe numbering.

In some embodiments, the encoding scheme of the coded light patterns ischosen to maximize processing flexibility in the surface reconstructionalgorithms. It can be advantageous for the encoding scheme to uniquelyencode the projector array pixels or pixel subregions in a manner thatfacilitates coded light calibration of each camera-projector stereopair, which allows code-light triangulation and rastersterographictriangulation methods to be employed for surface reconstruction. It isalso desirable in some datasets to employ spline fit surfacereconstruction methods which can leverage the column and row codevalues. Finally, by choosing parallel stripes with the properperiodicity, phase based square-wave reconstruction algorithms may alsobe employed. Each of these reconstruction techniques may be used aloneor in combination with one or more of the others to reconstruct thesurface of the desired three dimensional surface topography model.

Coded-light reconstruction refers specifically to the method ofcalculating three dimensional surface points from a series of structuredlight patterns which, when analyzed in its entirety, uniquely definesthe relationship between the pixels of the projected array and the threedimensional measurement region in which the ocular surface is situated.It can be performed by treating the pattern projection array as aninverse camera and triangulating between the pattern projection arrayand a given imaging detector. In this reconstruction method, a set ofcalibration coefficients is generated which uniquely define therelationship between a ray of light projected from a given pixel in thepattern projection system pixel array and the two dimensional pixelarray of the imaging detector, enabling algorithmic definition ofthree-dimensional points in space from the two-dimensional pixelcoordinates of the imaging detector when combined with the pixel codeinformation that uniquely encodes the pattern projection system pixels.

Rastersterographic reconstruction relies on direct triangulation betweentwo cameras which are calibrated as a stereographic pair, generating aset of calibration coefficients that uniquely defines the relationshipbetween the pixel coordinates of an incident light ray in camera 1 andthe pixel coordinates of an incident ray in camera 2 which come from thesame surface point in three dimensional space. In this reconstructionapproach the encoding sequences of the projected coded light patternsare used to index pixel correspondence between the two cameras in thestereographic pair, that is, to demonstrate that the light incident atone location in camera 1 came from the same point on the surface as theray of light incident at a second location in camera 2.

Slit-spline based surface reconstruction can be applied to anycombination of the structured light patterns used in the coded lightstructured light pattern sequence, including operations on single imageframes. This reconstruction technique may be applied using either orboth of the camera-projector stereo-calibration used in the coded lightreconstruction approach and the camera-camera stereo calibration used inthe rastersterographic reconstruction approach. In the slit-splineapproach, the Templated Grid Search is used to uniquely identify thestructured light pattern features evident in a single image frame.Spline fits to the pattern features are then combined with one or moreof the stereo calibrations to create a surface representation of theanterior ocular surface. When applied to full sets of capturedcoded-light image sequences, the slit-spline method is used to constrainand refine the results obtained from the coded-light andrastersterographic reconstructions. When the coded-light dataset isinterrupted by motion of the eye during the measurement, the slit splinereconstruction approach can be applied to subsets of the captured imagesequence to mitigate errors introduced by the ocular motion.

Phase-shift surface reconstruction uses Fourier analysis to measure thephase offsets between corresponding pixels in imaging elements of thestereo pairs. It can be used equally in conjunction with thecamera-projector stereo calibration used in the coded lightreconstruction method and to the camera-camera calibration used in therastersterographic reconstruction. The parallax phase differencesbetween the two imaging elements are used to calculate the threedimensional surface coordinates, and can be applied to single images,allowing it to be used to rescue datasets during which the eye has movedduring the projected pattern sequence. Additionally, for measurementscontaining a sequence of shifted phase-shifted square-wave patternswhere the eye remains stable during the measurement process, thephase-shift approach has the advantage of offering resolution beyond thepixel or row limits of the projected patterns (see Brenner 1999), so itcan be applied as supplemental processing to the coded-light andrastersterographic reconstruction methods to refine the model surfaces.

In one embodiment, a full three dimensional topographical model of theanterior ocular surface can be obtained from a single measurement takenwith the gaze direction of the eye fixed on a single fixation point. Inthis embodiment the lids of the eye are retracted manually by thepractitioner to expose the desired extent of the scleral and cornealregions of the anterior surface to be imaged. FIG. 12 shows a sample mapof the eye surface recorded with the eyelids mechanically retracted,viewed in profile 1201 and from a point on the optical axis 1202

In other embodiments, a full three dimensional topographical model ofthe anterior ocular surface is created as a composite model from aplurality of individual three dimensional topographical models of theanterior ocular surface where each individual three dimensionaltopographical model is calculated from a measurement taken with the eyefixed on each of a plurality of fixation points.

In one such embodiment, registration of the various topography models isaccomplished using feature information gleaned from flat-fieldillumination of the eye captured in conjunction with the coded lightpatterns. This can be done before or after using emission wavelength, orcan be done simultaneously by using non-overlapping light source andcolor camera.

In said embodiment Scale Invariant Feature Transform (SIFT) and BlockMatch (BM) algorithms are used to identify features on the scleralsurface and create a feature based description of each model whichorients it in space. Comparison of component features in each featurebased model description allows direct registration of models withrespect to one another. An iterative registration algorithm is then usedto refine the fit, where X, Y, Z components, and feature proximity areall used as optimization parameters.

The stitching registration process by which the individual threedimensional topography models are combined into a composite threedimensional topography model of the full extents of the anterior ocularsurface is depicted in FIG. 13. Each of the series of individual threedimensional topography models 1301 is analyzed 1302 to compute a roughorientation vector, from which the estimated overlap regions betweeneach model can be computed 1303, which are then used to determine theorder by which models will be registered to one another 1304. Inpractice, models with greater overlap are registered to each other, thensubsequent models are registered to the growing composite model. Thismaximizes the overlap between models at each registration step,increasing the reconstruction accuracy. The models comprising the seriesof individual three dimension topography models are then registered andstitched in a loop 1305 according to the calculated stitching order.Models u−1 1306 and u 1307 are registered to each other by using theircalculated feature descriptions 1308 and 1309 to identify the subset offeatures in each model feature description common to both models, andcomputing and applying a transform 1310 from the model u to model u−1.An iterative closest points algorithm 1312 is then applied whichoptimizes coefficients derived from matching nearest neighbors in eachmodel, using a coordinate space which includes X, Y, and Z threedimensional coordinates as well as color feature information as basisvectors. The stitched model then becomes model u−1, and the next modelin the series according to the computed stitching order takes the roleof model u. After registering all M models into a composite threedimensional topography model, additional iterations can be performedwhere each of the M models is compared to the composite model and it'sposition refined to minimize a weighting function. By tracking theweighting functions through successive iterations of looping through theM models, convergence can be determined. FIG. 14 depicts an example ofthe stitching process results for a series of measurement comprisingthree gaze directions. The flat-field illumination frames from thestructured light pattern illumination measurements 1401, 1403, and 1405are included to indicate the show direction of the eye relative to theimaging detector. The individual three dimensional topographical modelsresulting from the measurements at each gaze direction are displayed as1402, 1404, and 1406. The final stitched composite three dimensionaltopographical model is shown in 1407.

In said embodiment the registration process efficiency and robustness isaided by accurate estimation of the gaze orientation vector prior toapplication of nearest neighbor techniques such as feature matching oriterative closest points algorithms Accurate gaze estimation allowsestimation of overlap regions between models, allowing searchsegmentation. Such gaze estimation is accomplished by identifying thecorneal limbus by leveraging the contrast between the predominantlywhite sclera and the iris pigmentation. A plane can be fit to thethree-dimensional limbus points, for example using a least squarescriterion. The normal vector to the plane closely approximates the gazeorientation vector. The limbus plane is also used as a clipping plane toexclude features under the transparent corneal membrane, which aredistorted by the optical properties of said corneal membrane, from thefeature classification and matching algorithms.

In said embodiment speed and accuracy of the model registration processis enhanced by excluding all features not pertaining to the scleralsurface from the feature classification and matching algorithms. Aprimary interfering feature is represented by eyelashes which protrudeinto the optical path of the imaging detector. When a validcamera-camera triangulation pair is present eyelashes can be identifiedby generating disparity maps based on images obtained during flat-fieldillumination of the eye during the measurement process.

In some embodiments, full three dimensional topographical models of theanterior ocular surface can be created either by manually retracting thelids of the eye to expose the entire portion of the ocular surface to bemeasured or by combining a plurality of individual three dimensionaltopography models each containing some segment of the entire portion ofthe ocular surface to be measured into a composite three dimensionaltopographical model of the anterior ocular surface. To produce thecomposite topographical model, the technology can operate in distinctmodes: a Discrete Station Mode and a Continuous Processing Mode.

When said embodiment is operating in Discrete Station Mode, theoperation of the device is similar to the operation described previouslyand described in FIG. 9. In Discrete Station Mode, the steps 0902through 0908 are operated in a loop where each iteration of the loop isrealized by fixing gaze direction of the subject on a distinct elementof the gaze fixation target array. The modified process is depicted inFIG. 15, The image sequence comprising the data from each measurement ofthe ocular surface is then processed into an individual threedimensional topographical model by the computing device, and theplurality of individual three dimensional topographical models are thencombined into a composite model of the full extent of the anteriorocular surface portion measured.

When said embodiment is operating in Discrete Station Mode the locationsof the elements in the gaze fixation target array are chosen such thatthe portion of the ocular surface measured when the gaze direction isfixed on element N−1 overlaps significantly with the portion of theocular surface measured when the gaze direction is fixed on element N toallow optimal registration of individual models with respect to oneanother.

FIG. 16 details the Discrete Station Mode processing tree. Scan datacomprised of a sequence of images of the eye subject to a sequence ofstructured light patterns and flat-field illuminations is acquired for agiven gaze direction 1601. A stability check 1602 is then performed bycomparing flat-field illumination images comprising part of said patternsequence and a stability metric is calculated. If the stability metricmeets established criteria, the acquired data is processed through pathA, including surface point triangulation by means of Coded-lightreconstruction 1604 and Rastersterographic reconstruction 1605. Apreliminary feature classification is performed on each reconstructionresult 1606, and weighting coefficients and surface constraints areapplied to reconcile the various surface reconstructions 1607, beforethe flat-field illumination images are used in conjunction with SIFT andBlock Match algorithms to create a detailed feature-based compliment tothe three dimensional surface topology 1608 that is stored to thecomputer memory 1609 for future use.

If the stability metric 1602 fails to meet the established criteria, thedata is processed through path B which uses a combination of slit-splinereconstruction 1610 square wave phase-shift reconstruction 1611 onindividual image frames or pairs of image frames to mitigate the impactof eye motion by restricting the effective measurement windows to smallfractions of the entire measurement window. A feature classification isthen performed on each of the surface reconstructions 1612 using theflat-field illumination frame that preceded the structured lightsequence. The process then repeats using last two frames or frame pairsin the structured light sequence in conjunction with the flat-fieldframe that follows the structured light sequence. Namely, frames N−1 andN of the structured light sequence are processed using the slit-spline1613 and phase-shift reconstruction 1614 techniques and the featureclassifications are performed using the flat-field frame 1615. Thereconstruction results for Frames 1 and 2 are reconciled to each otherusing surface constraints and weighting coefficients 1616, and the sameprocess is applied to the results for Frames N−2 and N−1, before the tworeconciled results are combined and reconciled to one another 1618. Afinal feature classification step is performed to create thefeature-based compliment 1620 and the topology and feature informationare stored to the computer memory for future use 1621. In embodimentswhere flat-field illumination is acquired simultaneously with thestructured light pattern illumination data by using color cameras andnon-overlapping wavelength bands, each image frame or pair of imageframes in the acquire data image sequence may be processed as a separatemeasurement into a separate individual three dimensional topographymodel with its own feature-based compliment as well, as opposed toprocessing only the beginning and end portions of the sequence.

An additional processing path for this embodiment operating in DiscreteStation Mode is also available for real-time control of the measurementsystem hardware by the attached computing device. In said path C, if thestability metric fails to meet the established criteria, the data arere-acquired 1622.

When some embodiments are operating in Continuous Processing Mode, thedata acquisition and data processing functions are directly coupled bymeans of the attached computing device to improve data quality andmeasurement speed. In Continuous Processing Mode, the gaze fixationtarget array is initialized by the computer, then the ocular surface isilluminated by a flat-field illumination frame and a structured lightsequence truncated to one or a few frames of structured light patternsand image sequences of the illuminated ocular surface are captured bythe imaging sensors. The computer processes the acquired image sequenceinto an individual three dimensional topography model with afeature-based compliment description, orientation vector, and modelextents, then computes a desired gaze direction and updates theillumination of the gaze fixation target array. After each subsequentdata acquisition, convergence, coverage, and quality metrics arecalculated as part of the computation of the desired gaze direction forthe next acquisition. This process continues until the calculatedmetrics meet established criteria, and the controlling computeralgorithm ends the scan.

The operation of Continuous Processing Mode for this embodiment isdetailed in FIG. 17. The process begins with the subject's eye beingprepared with fluorescent dye 1701 and fixed on the gaze fixation targetarray in its initial state 1702. The controlling algorithm enters thecontrol loop 1703, during which it acquires image data by illuminatingthe eye with the structured light sequence and capturing images of theilluminate ocular surface 1704, processes the acquired image data usingthe Templated Grid Search algorithm 1705 and then applies one or both ofSlit-spline reconstruction and square wave phase reconstruction 1706,computes the feature-based description compliment and the coverage andquality metrics 1707, and reconciles the topology and feature results1708. For the first iteration of the loop, this reconciled topology andfeature result becomes the composite model, for subsequent iterations ofthe loop, the composite model is updated through another reconciliationprocess with the newly measured components 1709. Coverage and qualitymetrics are then calculated 1710 and compared against establishedcriteria 1711, after which a new gaze direction is determined andindicated on the fixation target array 1712, triggering the next scaniteration of the loop. For each measurement after the first, the newmeasurement is registered to the previous measurements by means of thefeature-based registration stitching method described previously. Theprocess repeats until the coverage and quality metrics meet theestablished convergence criteria.

In some embodiments, operating in Continuous Processing Mode offersspeed and data quality improvements by providing real-time feedback ondata quality and allowing the processing computer to correct fordeficiencies in the acquired data during the initial measurementprocess, minimizing the possibility of repeating the measurement at alater time. For embodiments which take advantage of color imagingsensors, the data quality and speed are both improved significantly bysimultaneous projection of the structured light pattern sequence andflat-field illumination frame using non-overlapping wavelength bands.

In some embodiments, a display screen attached to the computing devicedisplays provides operational feedback to the user. This feedbackincludes real-time views of the acquired imagery for use in alignmentand focusing of the measurement system with respect to the surface to bemeasured, intermediate stage progress indicators including focusingquality indicators, as well as visualizations of the three dimensionaltopographical models and optometrically useful realizations of saidmodels and quantities derived from them.

Additional embodiments can be used to create a three dimensional modelof the eye surface and electronically transmit it to the scleral andcontact lens manufacturing facility for designing and building a customlens that is specifically fit to a patient's eye.

Both the system and method embodiments disclosed herein may be usedindependently or in can be combined with a Placido disk based cornealtopography measurement within the same embodiment. In such embodiment,the traditional Placido disk measurement approach can be used to providea rapid corneal measurement without the fluorescent substance, while thestructured light system can be used for simultaneous measurement of theocular surface measurement in the corneal and scleral regions.Measurements made by either approach may stand alone, may be registeredinto a common data set to complement one another, or may be incorporatedas algorithmic constraints to one or both datasets to improve theaccuracy of a single composite model of the ocular surface. A schematicdrawing of the apparatus in a configuration allowing employment of bothPlacido disk and structured light stereo topographical measurementmethods for ocular surface measurement is shown in FIG. 18, where thepositions of the pattern projection system 1802 and the imagingdetectors 1803 and 1804, analogous to the pattern projection system 0305and imaging detectors 0301 and 0302 or the embodiment previouslydescribed, are modified so as to peer through openings in the Placidodisk assembly 1801, so as not to interfere with the Placido disk'scentral imaging detector 1805. This can be done with minimal impact onthe quality of the Placido disk measurement by choosing the openings inthe Placido disk assembly to coincide with dark, non-illuminated regionsof the disk assembly and by one-half-inch or other small diameteroptical assemblies for the pattern projection system and the imagingdetectors. In the apparatus depicted in FIG. 18 a simultaneousmeasurement using Placido disk and structured light is possible in orderto combine the two measurements to further increase the accuracy of theocular surface measurement.

Some examples of the disclosure may have more than two cameras arrangedin such fashion that more than three triangulation pairs can be createdduring the device operation and data analysis.

Additional Examples and Embodiments

In various embodiments, the systems and methods disclosed herein mayachieve one, some, or all of the following advantages and/or providesome or all of the following functionality.

In some embodiments, three simultaneous independent measurements areused, which may advantageously provide error reduction in overlapregions through averaging, error reduction in overlap regions throughconstraints, wider field-of-view by having cameras out at angles to thesurface to be measure, and/or more accurate tracking, because it may bedifficult to use corneal points for tracking.

In some embodiments, coded structured light is used to map the surfaceof the object (e.g., the anterior surface of the eye). Pattern sequencescan offer higher spatial resolution than single patterns, and uniquepixel encoding can eliminate iterative point searching, whichadvantageously can increase speed and/or accuracy of the mapping.

In some implementations, multiple patterns may be avoided because of eyemovements. Tracking and processing segmentation can allow for correctionfor eye movements. In some embodiments, trimming coded light bins tosingle stripes at bin edges can reduce dynamic range requirements and/orexposure modification requirements of the cameras. In some embodiments,trimming coded light sequence to moving set of identical patterns canprovide processing flexibility. For example, with smoothness constraintsfor the surface, the systems can perform true coded light methods.

Various implementations may provide multiple processing techniques. Forexample, the techniques can include Standard Coded Light (e.g., usingall frames or subset of frames), phase-shift or scanning slit usingsingle frames, etc. The systems and methods can be implemented to allowselection between techniques based on eye stability. Multiple techniquesto constrain solutions and improve surface accuracy can be adopted. Insome embodiments, use of identical patterns means each frame, or anysubset, can be processed by itself using alternate methods to battle eyemovement during the mapping sequence.

In various implementations, a fluorescent dye can be applied to theobject (e.g., the anterior surface of the eye) to deal with differencesin surface reflectivities. In some embodiments, real-timebrightness/quality indicator can be used to permit analysis of the dyecoverage and fluorescence intensity during focusing or mapping, andoptionally, after measurement. The systems and methods can be configuredto warn if scans need to be repeated.

The disclosed focusing methods of the camera and projector geometry mayallow a simple focusing/alignment indication by matching the projectedfocusing pattern with a fixed reference display pattern.

In some implementations, the measurements in multiple wavelengths allowobtaining position and intensity (e.g., XYZI) data. Such data may alloweye movement tracking, stitching registration of multiple partialdatasets (e.g., using intensity domain features to constrain algorithmsfor stitching smooth surfaces, limbus detection for scleral lensfitting, and/or detection of problem spots such as scaring to avoidduring scleral lens fitting.

In some implementations, simultaneous pattern projections in multiplewavelengths can be used. For example, flat field and structured lightcan be projected simultaneously. Red, green, blue (RGB) coded light iscan be used in ophthalmic or non-ophthalmic settings.

In some applications, substantially the entire sclera can be mapped bymoving the gaze direction, taking partial datasets, and then combiningthe datasets. In one example of a Discrete Station Mode, the systems andmethods utilize discrete gaze directions and the processing starts fromthe XYZI models collected (including third party data). In one exampleof Continuous Processing Mode, the systems and methods utilizeautomated, guided data acquisition. The gaze direction moves around infield following an indicator directed by the algorithm until convergenceis obtained.

In various implementations, any of the systems and methods disclosedherein can be combined with a Placido disk for two types of independentconical measurements.

Additional Examples of Aspects of the Disclosure

In a first aspect, a system for measuring an anterior surface topographyof an eye, the system comprising: a pattern projection system configuredto emit light towards an ocular surface of the eye, wherein the patternprojection system is configured to project a sequence of patterns ontothe ocular surface; one or more image sensors configured to record oneor more images of the patterns resulting from the projected patternsequence, an analysis system comprising computing hardware configured todetermine a topographic map of the ocular surface from the one or moreimages of the patterns.

In a 2nd aspect, the system of aspect 1, wherein the patterns in thesequence are projected in a single wavelength band.

In a 3rd aspect, the system of aspect 1 or aspect 2, wherein thepatterns in the sequence are projected in two or more wavelength bands.

In a 4th aspect, the system of any one of aspects 1-3, wherein one ormore patterns in the projected sequence of patterns are emitted in awavelength band at least partially overlapping an excitation wavelengthof a fluorescent substance adapted to be applied to the eye.

In a 5th aspect, the system of any one of aspects 1-4, wherein one ormore patterns in the projected sequence of patterns are emitted in awavelength band not overlapping an excitation wavelength of afluorescent substance adapted to be applied to the eye.

In a 6th aspect, the system of any one of aspects 1-5, wherein thepattern projection system is configured to produce structured lightpatterns in one or more of three modes which can be operated eithersimultaneously or sequentially, such that: in a first mode, an emittedwavelength range of the pattern projection system overlaps an excitationwavelength of a fluorescent substance used to prepare the ocular surfacebut does not overlap with a fluorescence wavelength of the fluorescentsubstance; in a second mode, an emitted wavelength range of the patternprojection system overlaps a fluorescence wavelength of a fluorescentsubstance used to prepare the ocular surface but does not overlap anexcitation wavelength of the fluorescent substance; and in a third mode,an emitted wavelength range of the pattern projection system overlapsneither an excitation wavelength of a fluorescent substance used toprepare the ocular surface nor a fluorescence wavelength of thefluorescent substance.

In a 7th aspect, the system of any one of aspects 1-6, wherein thesystem is configured to perform a measurement of the ocular surface in ameasurement duration less than about 0.5 seconds between themicrosaccadic movements of the eye.

In an 8th aspect, the system of aspect 7, wherein the pattern projectionsystem is configured to simultaneously project multiple individualpatterns from the sequence of patterns in a coded light sequence,wherein each individual pattern is projected in a non-overlappingwavelength band.

In a 9th aspect, the system of aspect 8, wherein the one or more imagesensors comprise a multi-color imaging detector configured to recordeach individual pattern in a separate recorded color channel, wherebysystem is configured to project and record the coded light sequence inone or more exposures.

In a 10th aspect, the system of any one of aspects 1-9, whereinillumination levels incident on the ocular surface are less than3.9×10⁻³ Joules of radiant energy as measured through a 7-mm aperturelocated within 5 mm of the projector focus.

In an 11th aspect, the system of any one of aspects 1-10, furthercomprising a fixation target system configured to permit a gaze of theeye to be sequentially fixed at a plurality of gaze directions.

In a 12th aspect, the system of aspect 11, wherein the fixation targetsystem comprises one or both of: a plurality of targets to beilluminated in sequence or an emissive screen configured to displaystationary or moving gaze fixation targets.

In a 13th aspect, the system of any one of aspects 1-12, furthercomprising a Placido disk corneal topographer system.

In a 14th aspect, the system of any one of aspects 1-13 wherein at leastone of the one or more image sensors is configured to simultaneouslyrecord at least one of the one or more images in a plurality ofwavelengths.

In a 15th aspect, the system of aspect 14, wherein the patternprojection system is configured to illuminate the ocular surface with aflat field in a first wavelength and one or more structured lightpatterns in second wavelength.

In a 16th aspect, the system of any one of aspects 1-15, furthercomprising a display device configured to display a representation ofthe topographic map of the ocular surface or a representation of one ormore optometric values derived from the topographic map.

In a 17th aspect, the system of any one of aspects 1-16, furthercomprising a scleral contact lens manufacturing system, wherein thesystem is configured to communicate information related to thetopographic map of the ocular surface to the scleral contact lensmanufacturing system.

In an 18th aspect, a method for calculating a three-dimensionaltopographical model of an anterior ocular surface of an eye, the methodcomprising: under control of an ocular topographic mapping systemcomprising computer hardware: receiving images of projected structuredlight patterns that are reflected or emitted from the anterior ocularsurface, the images obtained from a system comprising a plurality ofimaging sensors configured to record images projected on the anteriorocular surface by a pattern projection system; analyzing the receivedimages using one or more of the following techniques: coded lighttriangulation between any one of the plurality of imaging sensors andthe pattern projection system, or rastersterographic triangulationbetween any two of the plurality of imaging sensors, slit-spline surfacereconstruction, or phase-shift surface reconstruction; and determining,based at least in part on the analyzed images, a composite measurementof topography of at least a portion of the anterior ocular surface.

In a 19th aspect, the method of aspect 18, wherein determining thecomposite measurement of topography of at least a portion of theanterior ocular surface comprises combining a plurality of individualtopography measurements of portions of the anterior surface of the eyetaken at a plurality of orientations of an optical axis of the eye.

In a 20th aspect, the method of aspect 19, wherein each of the pluralityof individual topography measurements is created from a series of imagesof projected structured light pattern sequences reflected from theanterior ocular surface, wherein each pattern sequence comprises: atleast one image of the eye where the eye is illuminated in a wavelengthrange that overlaps a fluorescence wavelength of a fluorescent dye usedto prepare the ocular surface but does not overlap an excitationwavelength of the fluorescent dye, and at least one projected structuredlight pattern where the projected pattern is illuminated in a wavelengthrange that overlaps the excitation wavelength of the fluorescent dyeused to prepare the ocular surface but does not overlap the fluorescencewavelength of the fluorescent dye.

In a 21st aspect, the method of aspect 20, wherein determining thecomposite measurement of topography of at least a portion of theanterior ocular surface comprises: analyzing each of the plurality ofindividual topography measurements to provide a respective individualthree-dimensional topographical model of a segment of the ocularsurface, wherein the individual three-dimensional topographical modelcomprises three dimensional coordinate data, color intensity data, and afeature-based description of the individual three-dimensionaltopographical model produced from analyzing captured images of areflected or a fluorescent pattern sequence.

In a 22nd aspect, the method of any one of aspects 19-21, wherein eachof the plurality of individual topography measurements is taken in aDiscrete Station Mode wherein an individual topography measurement isacquired with an optical axis of the eye directed at one of a pluralityof fixed location fixation targets, wherein each individual topographymeasurement is created from a series of images of projected structuredlight pattern sequences reflected from the ocular surface, where eachpattern sequence comprises: at least two flat-field images of the eyewhere the eye is illuminated in a wavelength range that overlaps afluorescence wavelength of a fluorescent dye used to prepare the ocularsurface but does not overlap an excitation wavelength of the fluorescentdye, and a sequence of at least one projected structured light patternwhere the projected pattern is illuminated in wavelength range thatoverlaps the excitation wavelength of the fluorescent dye used toprepare the ocular surface but does not overlap the fluorescencewavelength of the fluorescent dye, and wherein at least one of the atleast two flat-field images of the eye precedes the sequence ofstructured light patterns, and at least one of the at least twoflat-field images of the eye follows the sequence of structured lightpatterns; and wherein the method further comprises processing each ofthe plurality of individual topography measurements into a respectiveindividual three-dimensional topography model.

In a 23rd aspect, the method of aspect 22, further comprising analyzingat least one of the flat-field images which preceded the sequence ofstructured light patterns and at least one of the flat-field imageswhich followed the structured light patterns to compute a metricdescribing apparent motion of the eye during a measurement period.

In a 24th aspect, the method of aspect 23, further comprisingdetermining, based at least in part on the computed metric, at least oneprocessing technique for constructing a respective individualthree-dimensional topographical model.

In a 25th aspect, the method of any one of aspects 19-24, wherein eachof the individual topography measurements is taken in ContinuousProcessing Mode wherein an individual topography measurement is acquiredand processed in a continuous loop until a desired convergence metric ora time threshold is reached, the method further comprising: computing acomposite three-dimensional topography model of the anterior ocularsurface from combinations of individual three-dimensional topographymeasurements acquired during the continuous loop in a measurementwindow, while the orientation of the eye is allowed to change during themeasurement window.

In a 26th aspect, the method of aspect 25, wherein each of theindividual topography measurements taken in Continuous Processing Modecomprises: at least one flat-field image of the eye where the eye isilluminated by a wavelength range that overlaps the fluorescencewavelength of the fluorescent dye used to prepare the ocular surface butdoes not overlap the excitation wavelength of the fluorescent dye, and asequence of at least one projected structured light patterns where theprojected pattern is illuminated in a wavelength range that overlaps theexcitation wavelength of the fluorescent dye used to prepare the ocularsurface but does not overlap the fluorescence wavelength of thefluorescent dye, the method further comprising: projecting the at leastone flat-field image and the sequence of at least one projectedstructured light patterns at least partially overlapped in time, if acolor camera is used, or projecting the at least one flat-field imageand the sequence of at least one projected structured light patternssequentially, if a monochromatic cameras is used.

In a 27th aspect, the method of aspect 26, further comprising:processing each of the individual topography measurements into a roughindividual three-dimensional topography along with extents andorientation of each rough individual three-dimensional topography model;combining each individual rough three-dimensional topography model withprevious rough three-dimensional topography models taken during ameasurement period of a subject into a rough composite three-dimensionaltopography model of a measured portion of the ocular surface; evaluatingthe extents and surface metrics of the measured portion of the ocularsurface to provide a gauge of measurement quality and completeness; andcommunicating the measurements of quality and completeness in real timesuch that a gaze direction of the subject can be adjusted to facilitatecompletion of the measurement of the eye of the subject.

In a 28th aspect, the method of any one of aspects 18-27, wherein theprojected structured light patterns comprise grids of parallel lines orsquare wave patterns.

In a 29th aspect, the method of any one of aspects 18-28 wherein theprojected structured light patterns are chosen to minimizeframe-to-frame variation of incident intensity of illumination strikingthe ocular surface.

In a 30th aspect, the method of any one of aspects 18-29, wherein theone or more of the following techniques comprise at least two of thetechniques, and the at least two techniques are applied to constrain orrefine the composite measurement of topography.

In a 31st aspect, the method of any one of aspects 18-30, furthercomprising: analyzing received images of reflected flat-fieldillumination to compute a feature-based description of individualthree-dimensional topographical models of the measured portion of theocular surface for registering the individual three-dimensionaltopographical models in Cartesian space; and analyzing, based at leastin part on the feature-based description, rotation and translation of anindividual three-dimensional topographical model with respect to anotherindividual three-dimensional topographical model or with respect to thatsame individual three-dimensional topographical model over the course ofthe measurement.

In a 32nd aspect, the method of aspect 31, wherein the feature-baseddescription contains points which correspond to the corneal limbus ofthe eye, the method further comprising creating a masking region whichexcludes non-topographical features in the corneal region from thefeature-based description of the individual three-dimensionaltopographical models to prevent optical properties of the cornea fromskewing the analysis of the rotation and translation of an individualthree-dimensional topographical model, and wherein a plane-fit to thecorneal limbus points is used to determine an approximate orientationfor the optical axis of the eye.

In a 33rd aspect, the method of any one of aspects 18-32, furthercomprising: receiving flat-field images captured simultaneously on morethan one of the plurality of imaging sensors; and determining regions ofthe images that are occluded in one or more received image by protrudingeyelashes.

Although descriptions of the embodiments herein have focused onmeasurement of the anterior surface of the human or animal eye, someembodiments of the technology may be equally applicable to themeasurement of surfaces of other objects of biologic or non-biologicnature.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “optical measurement head” does not imply that the components orfunctionality described or claimed as part of the optical measurementhead are all configured in a common package. Indeed, any or all of thevarious components of an optical measurement head, whether control logicor other components, can be combined in a single package or separatelymaintained and can further be distributed in multiple groupings orpackages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of example block diagrams, flow charts and other illustrations. Aswill become apparent to one of ordinary skill in the art after readingthis document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

While various embodiments of the present disclosure have been describedabove, it should be understood that they have been presented by way ofexample only, and not of limitation. Likewise, the various diagrams maydepict an example architectural or other configuration for thedisclosure, which is done to aid in understanding the features andfunctionality that can be included in the disclosure. The disclosure isnot restricted to the illustrated example architectures orconfigurations, but the desired features can be implemented using avariety of alternative architectures and configurations. Indeed, it willbe apparent to one of skill in the art how alternative functional,logical or physical partitioning and configurations can be implementedto implement the desired features of the present disclosure. Also, amultitude of different constituent module names other than thosedepicted herein can be applied to the various partitions. Additionally,with regard to flow diagrams, operational descriptions and methodclaims, the order in which the steps are presented herein shall notmandate that various embodiments be implemented to perform the recitedfunctionality in the same order unless the context dictates otherwise.

Each of the processes, methods, and algorithms described herein and/ordepicted in the attached figures may be embodied in, and fully orpartially automated by, code modules executed by one or more physicalcomputing systems, computer processors, application-specific circuitry,and/or electronic hardware configured to execute computer instructions.For example, computing systems can include general purpose computersconfigured with specific executable instructions for performing thedisclosed methods or special purpose computers, servers, desktopcomputers, laptop or notebook computers or tablets, personal mobilecomputing devices, mobile telephones, and so forth. A code module may bestored in non-transitory computer memory, compiled and linked into anexecutable program, installed in a dynamic link library, or may bewritten in an interpreted programming language. Further, certainimplementations of the functionality of the present disclosure aresufficiently mathematically, computationally, or technically complexthat application-specific hardware or one or more physical computingdevices (utilizing appropriate executable instructions) may be necessaryto perform the functionality, for example, due to the volume orcomplexity of the calculations involved (e.g., computing oculartopography) or to provide results substantially in real-time.

Code modules may be stored on any type of non-transitorycomputer-readable medium, such as physical computer storage includinghard drives, solid state memory, random access memory (RAM), read onlymemory (ROM), optical disc, volatile or non-volatile storage,combinations of the same and/or the like. The methods and modules mayalso be transmitted as generated data signals (e.g., as part of acarrier wave or other analog or digital propagated signal) on a varietyof computer-readable transmission mediums, including wireless-based andwired/cable-based mediums, and may take a variety of forms (e.g., aspart of a single or multiplexed analog signal, or as multiple discretedigital packets or frames). The results of the disclosed processes andprocess steps may be stored, persistently or otherwise, in any type ofnon-transitory, tangible computer storage or may be communicated via acomputer-readable transmission medium.

Any processes, blocks, states, steps, or functionalities in flowdiagrams described herein and/or depicted in the attached figures shouldbe understood as potentially representing code modules, segments, orportions of code which include one or more executable instructions forimplementing specific functions (e.g., logical or arithmetical) or stepsin the process. The various processes, blocks, states, steps, orfunctionalities can be combined, rearranged, added to, deleted from,modified, or otherwise changed from the illustrative examples providedherein. In some embodiments, additional or different computing systemsor code modules may perform some or all of the functionalities describedherein. The methods and processes described herein are also not limitedto any particular sequence, and the blocks, steps, or states relatingthereto can be performed in other sequences that are appropriate, forexample, in serial, in parallel, or in some other manner. Tasks orevents may be added to or removed from the disclosed exampleembodiments. Moreover, the separation of various system components inthe implementations described herein is for illustrative purposes andshould not be understood as requiring such separation in allimplementations. It should be understood that the described programcomponents, methods, and systems can generally be integrated together ina single computer or software product or packaged into multiple computeror software products. Many implementation variations are possible.

The processes, methods, and systems may be implemented in a network (ordistributed) computing environment. Network environments includeenterprise-wide computer networks, intranets, local area networks (LAN),wide area networks (WAN), personal area networks (PAN), cloud computingnetworks, crowd-sourced computing networks, the Internet, and the WorldWide Web. The network may be a wired or a wireless network (e.g., aterrestrial and/or satellite network) or any other type of communicationnetwork.

The various elements, features and processes described herein may beused independently of one another, or may be combined in various ways.All possible combinations and subcombinations are intended to fallwithin the scope of this disclosure. Further, nothing in the foregoingdescription is intended to imply that any particular feature, element,component, characteristic, step, module, method, process, task, or blockis necessary or indispensable. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements or components may be added to, removed from, orrearranged compared to the disclosed examples.

As used herein any reference to “one embodiment” or “some embodiments”or “an embodiment” means that a particular element, feature, structure,or characteristic described in connection with the embodiment isincluded in at least one embodiment. The appearances of the phrase “inone embodiment” in various places in the specification are notnecessarily all referring to the same embodiment. Conditional languageused herein, such as, among others, “can,” “could,” “might,” “may,”“e.g.,” and the like, unless specifically stated otherwise, or otherwiseunderstood within the context as used, is generally intended to conveythat certain embodiments include, while other embodiments do notinclude, certain features, elements and/or steps. In addition, thearticles “a” or “an” as used in this application and the appended claimsare to be construed to mean “one or more” or “at least one” unlessspecified otherwise.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having” or any other variation thereof, areopen-ended terms and intended to cover a non-exclusive inclusion. Forexample, a process, method, article, or apparatus that comprises a listof elements is not necessarily limited to only those elements but mayinclude other elements not expressly listed or inherent to such process,method, article, or apparatus. Further, unless expressly stated to thecontrary, “or” refers to an inclusive or and not to an exclusive or. Forexample, a condition A or B is satisfied by any one of the following: Ais true (or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), or both A and B are true (orpresent). As used herein, a phrase referring to “at least one of” a listof items refers to any combination of those items, including singlemembers. As an example, “at least one of: A, B, or C” is intended tocover: A, B, C, A and B, A and C, B and C, and A, B, and C. Conjunctivelanguage such as the phrase “at least one of X, Y and Z,” unlessspecifically stated otherwise, is otherwise understood with the contextas used in general to convey that an item, term, etc. may be at leastone of X, Y or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require at least one of X, atleast one of Y, and at least one of Z to each be present.

Although the disclosure is described above in terms of various exemplaryembodiments and implementations, it should be understood that thevarious features, aspects and functionality described in one or more ofthe individual embodiments are not limited in their applicability to theparticular embodiment with which they are described, but instead can beapplied, alone or in various combinations, to one or more of the otherembodiments of the disclosure, whether or not such embodiments aredescribed and whether or not such features are presented as being a partof a described embodiment. Thus, the breadth and scope of the presentdisclosure should not be limited by any of the above-described exemplaryembodiments.

1. (canceled)
 2. A system for measuring an anterior surface topographyof an eye, the system comprising: a projection system configured to emitlight towards an ocular surface of the eye and to project a singlepattern or a sequence of patterns onto the ocular surface; an imagesensor configured to record one or more images of the patterns resultingfrom the projected pattern or sequence, an analysis system comprisingcomputing hardware configured to determine a topographic map of theocular surface from the one or more images of the patterns, wherein theanalysis system is configured to obtain measurements of a plurality ofsegments of the ocular surface and to combine the measurements into asingle measurement covering an area larger than the measured segments.3. The system of claim 2, further comprising a fixation target systemconfigured to permit a gaze of the eye to be sequentially fixed at aplurality of gaze directions.
 4. The system of claim 3, wherein thefixation target system comprises one or more of: a plurality of targetsto be illuminated in sequence, an emissive screen configured to displaystationary or moving gaze fixation targets, or one or more targets thatcan be physically moved to direct the gaze to a specified direction. 5.The system of claim 2, wherein the single measurement includes regionsof the ocular surface normally hidden by an eyelid.
 6. The system ofclaim 2, wherein the system is configured to analyze the informationrelated to the topographic map of the ocular surface for a design of acontact lens for the measured eye.
 7. The system of claim 6, wherein thecontact lens is a scleral contact lens.
 8. The system of claim 2,wherein the system is configured to analyze information related to thetopographic map of the ocular surface and to predict a fit of a contactlens on the eye.
 9. The system of claim 8, wherein the contact lens is ascleral contact lens.
 10. The system of claim 2, wherein the system isconfigured to communicate information related to the topographic map ofthe ocular surface to a contact lens manufacturing system formanufacturing of a custom fit contact lens.
 11. The system of claim 10,wherein the custom fit contact lens is a scleral contact lens.
 12. Thesystem of claim 2, wherein the projection system comprises a singleprojector and the image sensor comprises one or more image sensors. 13.A method for calculating a three-dimensional topographical model of ananterior ocular surface of an eye, the method comprising: under controlof an ocular topographic mapping system comprising computer hardware:receiving images of projected patterns that are reflected or emittedfrom the anterior ocular surface; analyzing the received images; anddetermining, based at least in part on the analyzed images, a compositemeasurement of topography of at least a portion of the anterior ocularsurface, wherein the composite measurement comprises measurement of atleast one region of the anterior ocular surface that is hidden by aneyelid in at least one of the received images.
 14. The method of claim13, wherein determining the composite measurement of topography of atleast a portion of the anterior ocular surface comprises combining aplurality of individual topography measurements of portions of theanterior surface of the eye taken at a plurality of orientations of anoptical axis of the eye.
 15. The method of claim 14, further comprisingdetermining the plurality of orientations of the optical axis of the eyeby at least one of the following: obtaining a location of a gazefixation target; analyzing a 3-dimensional topography of the anteriorsurface of the eye; or analyzing a 3-dimensional orientation of a knownanatomical structure of the eye.
 16. The method of claim 15, wherein theanatomical structure of the eye comprises the corneal limbus.
 17. Themethod of claim 15, wherein the anatomical structure of the eyecomprises the pupil.
 18. The method of claim 14, wherein determining theplurality of optical axis orientations comprises using one or both of:evaluating an automated computer algorithm, or receiving input from anoperator of the ocular topographic mapping system.
 19. The method ofclaim 18, wherein determining the plurality of optical axis orientationscomprises receiving a location of the corneal limbus determined by theoperator of the ocular topographic mapping system.
 20. The method ofclaim 14, wherein combining the plurality of individual topographymeasurements comprises determining boundaries of the individualtopography measurements using an automated algorithm.
 21. The method ofclaim 14, wherein combining the plurality of individual topographymeasurements comprises receiving information relating to boundaries ofthe individual topography measurements obtained by an operator of theocular topographic mapping system.